The city-state Governors Island Preservation and Education Corp. yesterday tossed out all proposals from developers vying to turn the former military base into a tourist attraction, including cable-TV giant Nickelodeon’s plan to create a children’s theme park there.

The decision means a master developer for the long-dormant 172-acre island won’t be selected “for quite a while,” said Deputy Mayor Dan Doctoroff, declining to be specific.

Instead, GIPEC is shifting its immediate focus toward improving island transportation, creating new parkland and finding tenants for historic buildings on the north end.

Despite the development setback, the island’s first anticipated new tenant was announced yesterday. The New York Harbor School, a Brooklyn high-school specializing in maritime studies, will make Governors Island its new home once details are finalized between GIPEC and the city’s Education Department, officials said.

Doctoroff, who chairs GIPEC, said none of the major development proposals solicited was “financially feasible,” but he was still optimistic about the island’s future.

“I don’t see this as going back to the drawing board,” said Doctoroff, adding that GIPEC’s immediate goal is making the island more attractive for future development.

City and state officials have openly talked about bringing hotels, conference centers, marinas, an amphitheater and other attractions to the island – all of which are now on hold.

GIPEC in August narrowed the list of prospective developers from 25 to 10, but rejected all of them except the Harbor School plan, which will only use a small portion of the island. As The Post reported in January, the city and state still hope to drum up interest in the island by building a $125 million aerial gondola system connecting it with both Brooklyn and lower Manhattan.

Currently, the only way onto the island is by ferry from Manhattan’s Battery Marine Terminal, but that soon should change. GIPEC President Leslie Koch said a floating barge would be built on the north end, allowing private water taxis to dock there by next summer.

GIPEC is now reviewing qualifications of top landscape architects and urban planners seeking the plum job of designing a 25- to 40-acre megapark on the southwestern end that would provide grand access to the most direct view by land of the Statue of Liberty.

That project also includes a 14-acre esplanade circling the island and pocket parks in the north end.